Studies are being conducted on the manner in which the epidermal structures of the adult head of Drosophila are determined by events occurring from the blastoderm stage of development to differentiation of the cells of the head anlage at metamorphosis. Clonal analysis is undertaken by induced somatic recombination in appropriate heterozygotes and clonal restrictions are analyzed by using the differential multiplication of wild-type cells in a background of Minute cells. The homeotic mutants of opthalmoptera and antennapedia are also being used in the analysis of head development.